The overall aim of this proposal is to better understand the role of cell-matrix interactions in the formation, organization and maintenance of the chondrocyte pericellular matrix. During the past several years we have discovered the exquisite coordination between the expression of hyaluronate binding sites and the onset of limb chondrogenesis. This precise timing is suggestive of an important role of this putative hyaluronate receptor in this process, Our new preliminary results have also led us to put forth the hypothesis that cell-associated hyaluronate, especially receptor-bound hyaluronate, serves as the anchor of the pericellular matrix to the chondrocyte cell surface. This hypothesis will be tested using three cell-model systems derived from different stages during chondrogenesis in the limb. Initially, in order to better characterize this hyaluronate binding site/receptor, binding parameters including the number of sites/cell, their affinity, specificity of the binding, and the minimum length of hyaluronate that can interact with the binding site, will bc determined. Using reagents which specifically block these putative hyaluronate receptors we will determine: 1) whether hyaluronate is, in fact, the anchor of the pericellular matrix to the cell surface; 2) does receptor bound or non-receptor-bound hyaluronate participate in the assembly of a pericellular matrix and; 3) is aggregating proteoglycan, via its association with cell surface hyaluronate the primary component involved in pericellular matrix assembly. Using regrowth experiments in the presence of blocked or unblocked hyaluronate receptors, questions concerning the kinetics of assembly as well as the distribution of newly synthesized hyaluronate and proteoglycan into the pericellular matrix, will be addressed. The pericellular matrix represents an interface at which chondrocytes initiate and perhaps control matrix assembly. An understanding of the mechanisms of matrix organization will help us to understand changes in the matrix during remodeling, degradation and repair of articular cartilage that occur during the progression of degenerative arthritis. This project forms the part of the long-term goals of the Principal Investigator to understand the role of cell-matrix interactions in developing, aging and degenerative tissue systems.